1. Field of the Invention
The present invention relates to a radar system mounted in a vehicle and more particularly to a vehicle radar system utilized in an ACC (Active Cruise Control) system, a pre-crash system, or the like.
2. Description of the Related Art
To date, as an apparatus for preventing a crash between vehicles or between a vehicle and an object in front, a vehicle rear-end accident, and the like before they occur, or as an apparatus for reducing impact damage to occupants when these crashes occur, there have been proposed a great number of apparatuses in which the degree of the risk of a crash between a reference vehicle and an object in front is determined and in accordance with the degree of the risk, a predetermined control unit is operated so that the crash is prevented or crash damage is reduced. In general, in these conventional apparatuses, as a unit for detecting an object in front of a vehicle, a vehicle radar system such as a millimeter wave radar or a laser radar is utilized.
For example, a millimeter wave radar is capable of detecting the relative distance or the relative speed between a reference vehicle and an object in front. Accordingly, by comparing the speed of the reference vehicle with the relative speed between the reference vehicle and the object in front, the millimeter wave radar can determine whether the object in front is moving or stationary. In this case, the stationary object denotes an object, such as a stationary vehicle, a telephone or a road-sign pole, or a pedestrian, which could often be an obstacle to the travel of the reference vehicle. However, in the objects that are to be detected as being stationary, there is included an object, such as a manhole cover or an empty can placed on a road, which does not bring about any trouble to the travel of the reference vehicle even when the reference vehicle passes over or under it.
However, considering the detection performance of a millimeter wave radar, it is extremely difficult to distinguish object types; therefore, in some times, the foregoing crash damage reducing apparatus utilizing a millimeter wave radar erroneously operates at a timing unintended by the driver, in response to an object that cannot be an obstacle in fact.
As an apparatus that solves these problems, for example, there has been disclosed an object detection apparatus (e.g., refer to Patent Document 1) in which a laser beam is irradiated forward in such a way that the irradiation region of an upward irradiation wave to be irradiated upward and the irradiation region of a downward irradiation wave to be irradiated downward partly overlap with each other, and based on the respective reflection intensities of the upward irradiation wave and the downward irradiation wave, the type of the object on which the irradiation waves have reflected is determined.